The present invention relates to moulded objects of alumina matter-containing raw materials for aluminum smelting by a blast furnace method. Further, alumina matter described in this specification means alumina contained in bauxite or clay, aluminum hydroxide and an alumina component in composite aluminum oxides.
Aluminum is a fundamental metallic material next to iron and its demands are increasing in a high ratio year by year. However, due to an increase in energy cost on a worldwide scale in recent years, aluminum manufacturing in areas such as Japan where electric power cost is high has become very difficult and countries in such areas are incurring serious hindrances to their industrial structure. In addition, areas enabling the locating of a cheap hydro-electric power source therein are expected to be increasingly narrowed in the world hereafter. Therefore, development of an energy-saving and low-cost manufacturing process for the smelting of aluminum that is an important industrial material is being demanded as an urgent problem.
Bayer-Hall-Heroult process that is a conventional aluminum smelting process comprises 1 Bayer process that is a process for extracting alumina from bauxite and 2 Hall-Heroult process that is an electrolytic process. The former process requires extraction and crystallization steps taking a long time so that it has low productivity and results in high equipment cost, and the latter process is an electrolytic process so that it has no merit of plant scaling up, has low productivity and high equipment cost and requires a large amount of electric power. Thus, Bayer-Hall-Heroult process has many industrial demerits as mentioned above and also has already scarcely room for its technical improvement, so that appearance of a drastic new process for aluminum smelting is being demanded.
In order to eliminate such demerits of Bayer-Hall-Heroult process, various alternative smelting processes including an electric furnace reducing process have been studied. However, these processes succeeded neither in energy saving effect nor in a decrease in cost enough to replace the conventional process. As demerits of these alternative processes, there can be cited for example the required electric power similar to or more than that of the conventional process, which is seen in the electric furnace reducing process, and a great amount of energy and much cost that are required for the treatment of raw materials in the electrolytic process of aluminum chloride.
On the other hand, as a method for eliminating the above-mentioned demerits of the conventional aluminum smelting process consuming a lot of electric power, an aluminum smelting process by a blast furnace method for reducing alumina matter-containing raw materials with carbon materials using a blast furnace of counter-current moving bed type has become examined in recent years.
In this process, a packed layer comprising raw materials containing alumina matter and a carbon material acting as a fuel and a reducing agent is formed in a blast furnace and the following combustion reaction (1) and reduction reaction (2) are conducted at the same time in the furnace. EQU C+1/2 O.sub.2 .fwdarw.2 CO (1) EQU Al.sub.2 O.sub.3 +3 C.fwdarw.2 Al+3 CO (2)
Reduction of aluminum oxide (alumina matter) represented by Formula (2) is carried out by employing the heat of oxygen combustion of the carbon materials represented by Formula (1) as a heat source for the reduction reaction. Further, the blast furnace is of counter-current moving bed type. At the same time oxygen gas is blown into the furnace at its lower part, a reduction product is taken out of the bottom part of the furnace. Corresponding to the discharge of product, feed raw materials are charged into the furnace through its top, and thus the whole packed layer transfers downward being in counter-current contact with the combustion gas.
When the above-mentioned reactions (1) and (2) are carried out at the same time in a blast furnace to smelt aluminum by a blast furnace method, there are existing various technical problems to be solved for the economical efficiency and workability of the method. In particular, there can be cited the problem of blockade of the furnace and a lowering in aluminum yield that is caused by the evolution and condensation of volatile aluminum components (Al.sub.2 O and Al) and a volatile silicon component (SiO).
To restrain the evolution of such volatile aluminum components and of such a volatile silicon component, an alloyable component such as iron or the like is ordinarily added to alumina matter-containing raw materials to lower the reducing temperature for alumina. Thus, there has been adopted a method for improving the formation of metallic aluminum by the above-mentioned addition of an alloyable component to lower the reduction reaction temperature and also to stabilize the formed metallic aluminum by transforming it into an alloy. However, it is difficult to restrain completely the evolution of such volatile substances even by such a method.
In addition, in such a blast furnace method, there is also known a process for feeding alumina matter-containing raw materials into a blast furnace in the form of massive ores comprising the raw materials and a carbon material for the purpose of improving the contact between the reducing agent and alumina matter to raise the rate of reduction reaction or of effectively utilizing powdered raw materials and coke.
However, the process for feeding the raw materials into a blast furnace in the form of massive ores as mentioned above scarcely had the effect of restraining the evolution of the above-mentioned volatile substances and also had the defect of causing a slagging agent for liquating out ash matter contained in a carbon material for fuel to melt with alumina matter-containing raw materials before the materials were subjected to the reduction reaction and of making the alumina matter-containing raw materials difficult to reduce.